Would 'sectioned' be used then in France, it struck me as a UK expression, we say 'committed'. I would eliminate the authorial presence, when you talk about her art, Rodin, her brother, it makes the poem too objective, I like the poem when it focuses on her actual situation. I don't think you need to mention who she is, if people don't know, well they should. You say young brother, I assume that's deliberate, meaning he was young when he said it.

A lot to like here. I'm partial to the first half of the poem. For me, it's more effective to see the portrait, what she's doing, than to be told her thoughts. I've never heard the term "sectioned" in this context (I'm in the US).